The present invention relates to an apparatus for controlling a power source of a wire electric discharge machine, and more particularly, to an electric discharge machining control apparatus capable of effecting straight machining, corner machining, and arcuate machining in a stable manner, with improved accuracy.
Presently, many wire electric discharge machines use water as a machining fluid. In this case, a leakage current is produced between a wire electrode and a workpiece in accordance with a gap resistance therebetween, whereby electrolysis is effected. In rough machining, the leakage current does not raise any special problem because electric discharge energy is great. In finish machining, however, if the electric discharge energy for each cycle is large, the machined surface of the workpiece is too rough. In order to minimize surface roughness, therefore, the electric discharge energy must be reduced. If the electric discharge energy is too small, however, stable electric discharge cannot be maintained due to the aforesaid leakage current.
In corner machining or arcuate machining for concave portions, the gap resistance is lower, and more leakage current flows than in straight machining, resulting in too small electric discharge energy which permits unstable electric discharge. Conventionally, therefore, electrical conditions, such as current, supply voltage, on/off time for capacitor charge and discharge in a capacitor discharge circuit, etc., are adjusted during corner machining such that the gap resistance is low, and the leakage current is substantial.
If straight machining is performed under electrical conditions such that stable electric discharge can be obtained and the roughness of the machined surface is satisfactory in the corner machining process for concave portions, the electric discharge energy increases due to less leakage current than in the corner machining, so that the machined surface roughness worsens.